Battery management apparatus, battery management method, and battery energy storage system

ABSTRACT

A battery management apparatus  102  is an apparatus which manages a chargeable and dischargeable battery, and includes: a battery state calculation unit  501  which calculates a state of charge SOC representing the state of charge of the battery, and a charge capacity fade SOHQ representing a deterioration degree; a mid voltage calculation unit  502  which calculates a mid voltage that is present between the discharge voltage in a current state of charge of the battery, and a voltage value representing the discharge voltage in a minimum state of charge of the battery; a remaining capacity calculation unit  503  which calculates a remaining capacity of the battery, based on the state of charge SOC and the charge capacity fade SOHQ; and an available energy calculation unit  504  which calculates available energy of the battery, based on the mid voltage and the remaining capacity.

TECHNICAL FIELD

The present invention relates to a battery management apparatus, abattery management method, and a battery energy storage system.

BACKGROUND ART

In recent years, in view of the global warming problem, there has beenan increased use of a power generation and transmission system that isintended to generate power by using renewable energy, such as sunlightand wind power, and stabilize the output by using a battery energystorage system (BESS). In view of emission control, such a batteryenergy storage system is widely used also for a mobile traffic system,such as of automobiles.

A conventional, typical battery energy storage system includes: abattery that includes multiple battery cells combined with each other; acooling system that cools the battery to regulate the temperature; abattery management apparatus that performs charge and discharge controland maintains the system in a safe state.

Battery energy storage systems mounted on electric vehicles, hybridvehicles and the like are required to correctly obtain battery states,such as a state of charge (SOC), a state of health (SOH), and themaximum permissible power, in order to facilitate to optimize vehiclecontrol while maintaining the battery in the safe state. These batterystates are obtained based on measured values, such as current, voltageand temperature, through sensors. One of the battery states used forsuch battery energy storage systems is available energy. The availableenergy represents the total amount of electrical energy remaining in thebattery, and corresponds to electrical energy that can be dischargeduntil the battery reaches a permissible use limit. The available energyis used to calculate the travelable distance of a vehicle until thebattery reaches a fully discharged (use limit) state, for example.

As for calculation of the available energy of a battery, a techniquedescribed in Patent Literature 1 has been known. Patent Literature 1discloses a method including: obtaining a battery's initial availableenergy; calculating the battery's accumulative consumption energyconsumed while a vehicle is travelling a current accumulative drivingdistance; calculating the battery's remaining available energy fromthese values; calculating a final electric efficiency corresponding todriving the current accumulative driving distance; and calculating atravelable distance of the vehicle.

CITATION LIST Patent Literature

[Patent Literature 1]

-   U.S. Pat. No. 9,037,327

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

According to the method in Patent Literature 1, during calculation ofthe accumulative consumption energy of the battery, the errors of avoltage sensor and a current sensor are accumulated. Accordingly, inparticular, after the vehicle travels a long distance, it is difficultto correctly estimate the available energy of the battery.

Means to Solve the Problems

A battery management apparatus according to the present inventionmanages a chargeable and dischargeable battery, and includes: a batterystate calculation unit which calculates a state of charge and adeterioration degree of the battery; a mid voltage calculation unitwhich calculates a mid voltage that is present between acharge-discharge voltage in a current state of charge of the battery,and a charge-discharge voltage in a minimum state of charge or a maximumstate of charge of the battery; a remaining capacity calculation unitwhich calculates a remaining capacity or a chargeable capacity of thebattery, based on the state of charge and the deterioration degree; andan available energy calculation unit which calculates available energyor chargeable energy of the battery, based on the mid voltage and theremaining capacity, or on the mid voltage and the chargeable capacity.

A battery management method according to the present invention is amethod for managing a chargeable and dischargeable battery, the methodincluding, by a computer: calculating a state of charge and adeterioration degree of the battery; calculating a mid voltage that ispresent between a charge-discharge voltage in a current state of chargeof the battery, and a charge-discharge voltage in a minimum state ofcharge or a maximum state of charge of the battery; calculating aremaining capacity or a chargeable capacity of the battery, based on thecalculated state of charge and deterioration degree; and calculatingavailable energy or chargeable energy of the battery, based on thecalculated mid voltage and remaining capacity, or on the calculated midvoltage and chargeable capacity.

A battery energy storage system according to the present inventionincludes: the battery management apparatus; a chargeable anddischargeable battery; and a charge-discharge apparatus which chargesand discharges the battery, based on available energy or chargeableenergy of the battery calculated by the battery management apparatus.

Advantageous Effects of the Invention

The present invention can correctly estimate the available energy of thebattery.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic configuration diagram of a battery energy storagesystem according to one embodiment of the present invention.

FIG. 2 illustrates available energy.

FIG. 3 is a concept diagram of a method of calculating the availableenergy according to the present invention.

FIG. 4 shows functional blocks of the battery management apparatuspertaining to an available energy calculation process according to afirst embodiment of the present invention.

FIG. 5 shows functional blocks of a battery state calculation unit.

FIG. 6 shows an example of an equivalent circuit of a battery cell in abattery model.

FIG. 7 shows functional blocks of a mid voltage calculation unitaccording to the first embodiment of the present invention.

FIG. 8 shows functional blocks of the battery management apparatuspertaining to an available energy calculation process according to asecond embodiment of the present invention.

FIG. 9 shows functional blocks of a mid voltage calculation unitaccording to the second embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention are hereinafter described.

First Embodiment

FIG. 1 is a schematic configuration diagram of a battery energy storagesystem according to one embodiment of the present invention. The batteryenergy storage system (BESS) 1 shown in FIG. 1 includes an assembledbattery 101, a battery management apparatus 102, a current sensor 103, acell controller 104, a voltage sensor 105, a temperature sensor 106, andrelays 107. The battery energy storage system 1 is coupled to a load 3,such as an AC motor, via an inverter 2. The battery energy storagesystem 1 and the inverter 2 are coupled to an upper level controller 4via a communication circuit, not shown.

The assembled battery 101 includes multiple chargeable and dischargeablebattery cells coupled in series and in parallel. For drive operation ofthe load 3, DC power discharged from the assembled battery 101 isconverted by the inverter 2 into AC power, and is supplied to the load3. For regenerative operation of the load 3, AC power output from theload 3 is converted by the inverter 2 into DC power, with which theassembled battery 101 is charged. Such operation of the inverter 2charges and discharges the assembled battery 101. The operation of theinverter 2 is controlled by the upper level controller 4.

The current sensor 103 detects current flowing in the assembled battery101, and outputs the detection result to the battery managementapparatus 102. The cell controller 104 detects the voltage of eachbattery cell of the assembled battery 101, and outputs the detectionresult to the battery management apparatus 102. The voltage sensor 105detects the voltage (total voltage) of the assembled battery 101, andoutputs the detection result to the battery management apparatus 102.The temperature sensor 106 detects the temperature of the assembledbattery 101, and outputs the detection result to the battery managementapparatus 102. The relays 107 switches the coupling state between thebattery energy storage system 1 and the inverter 2 according to controlby the upper level controller 4.

The battery management apparatus 102 controls charge and discharge ofthe assembled battery 101 based on the detection results of the currentsensor 103, the cell controller 104, the voltage sensor 105 and thetemperature sensor 106. At this time, the battery management apparatus102 calculates various types of battery states as indicators whichindicate the states of the assembled battery 101. The battery statescalculated by the battery management apparatus 102 include, for example,the state of charge (SOC), state of health (SOH), maximum permissiblepower, and available energy. By controlling the charge and discharge ofthe assembled battery 101 by using these battery states, the batterymanagement apparatus 102 safely controls the assembled battery 101. As aresult, an upper level system (an electric vehicle, a hybrid vehicle,etc.) provided with the battery energy storage system 1 can beefficiently controlled. The battery management apparatus 102 performsinformation communication required to control the charge and dischargeof the assembled battery 101, with the upper level controller 4.

Note that in this embodiment, the available energy described above isdefined as the total amount of electrical energy that the assembledbattery 101 can discharge, in the electrical energy accumulated in theassembled battery 101. This corresponds to the total electric energy(Wh) dischargeable without each battery cell falling below the minimumvoltage V_(min), until the SOC of each battery cell reaches SOC_(min),which is the minimum SOC value permitted for the corresponding batterycell, in a case where each battery cell of the assembled battery 101 isdischarged with a constant discharge current I_(C0,DCh). Note that thedischarge current value I_(C0,DCh) is preset depending on the operationmode and the like of the battery energy storage system 1.

FIG. 2 illustrates the available energy. In FIG. 2, a broken lineindicated by a symbol 700 represents an SOC-OCV curve that indicates therelationship between the SOC and the open-circuit voltage (OCV) of eachbattery cell of the assembled battery 101. A solid line indicated by asymbol 701 represents a discharge curve when each battery cell of theassembled battery 101 is discharged with the constant discharge currentI_(C0,DCh) from the current SOC to SOC_(min). Note that in FIG. 2, thecurrent SOC is indicated by a broken line 703, and the SOC_(min) isindicated by a broken line 705.

The discharge curve 701 indicates the relationship between the SOC andthe closed-circuit voltage (CCV) during discharge from each battery cellof the assembled battery 101. That is, the CCV of each battery cellduring discharge of the assembled battery 101 continuously changes,according to the discharge curve 701, from the voltage value 704corresponding to the current SOC to the voltage value 706 correspondingto SOC_(min) when discharge is finished, in a range where theclosed-circuit voltage does not fall below the minimum voltage V_(min)indicated by a broken line 707.

Here, provided that the C-rate during discharge corresponding to thedischarge curve 701 is represented as C₀, the discharge currentI_(C0,DCh) can be represented as I_(C0,DCh)=C₀×Ah_(rated). In thisexpression, Ah_(rated) represents the rated capacity of each batterycell.

The available energy of each battery cell during discharge is defined bythe following (Expression 1).

[Expression 1]

In (Expression 1), CCV(t) represents the CCV of each battery cell at atime t, i.e., the value of a discharge voltage, t_(present) representsthe current time, and t_(end) represents a time when the SOC of eachbattery cell reaches SOC_(min) and discharge is finished. This(Expression 1) represents the integral value of the discharge curve 701from the current SOC to SOC_(min) shown in FIG. 2. That is, in FIG. 2,the area of an area 702 that is encircled by the discharge curve 701 andthe broken lines 703 and 705 and is indicated by hatching corresponds tothe available energy of each battery cell.

For example, in a case where the battery energy storage system 1 ismounted on a vehicle, the available energy of the assembled battery 101is required to be calculated in real time in order to achieveappropriate and safe vehicle control. However, during vehicle traveling,the current sequentially changes. Consequently, (Expression 1), which isa calculation expression assuming a constant discharge currentI_(C0,DCh), cannot be applied. In the present invention, according to acalculation method described below, the available energy of theassembled battery 101 can be directly calculated in real time withoutusing (Expression 1).

FIG. 3 is a concept diagram of a method of calculating the availableenergy according to the present invention. In FIG. 3, the SOC-OCV curve700 and the discharge curve 701 correspond to those in FIG. 2. In FIG.3, in addition to these curves, an area 708 indicated by hatching isdepicted. The area 708 is defined as the remaining capacity of eachbattery cell, i.e., the area of a rectangle having a long side that is adifference ΔSOC between the current SOC and SOC_(min), and a short sidethat is a mid voltage 710 that is present between the voltage value 704corresponding to the current SOC on the discharge curve 701 and thevoltage value 706 corresponding to the SOC_(min) when discharge isfinished.

In the present invention, the mid voltage 710 that is present on thedischarge curve 701 is obtained such that the area of the area 708 inFIG. 3 matches the area of the area 702 in FIG. 2. Accordingly, the areaof the rectangular area 708 by multiplying the mid voltage 710 by theremaining capacity (ΔSOC), thereby allowing the area of this area 702 inFIG. 2, i.e., the available energy, to be calculated.

Note that in FIG. 3, a point 709 on the SOC-OCV curve 700 represents theOCV value (mid OCV) corresponding to the mid voltage 710. The mid OCV ispresent between the OCV value in the current SOC and the OCV value inthe SOC_(min). A point 711 on the abscissa axis represents a SOC value(mid SOC) corresponding to the mid voltage 710 and the mid OCV. The midSOC is present between the current SOC and the SOC_(min).

The method of calculating the available energy for units of batterycells has been described above. In this embodiment, it is preferable tocalculate the available energy for the entire assembled battery 101. Forexample, for each of the battery cells constituting the assembledbattery 101, the available energy is calculated with respect to eachbattery cell, and the calculation results of the available energy of theindividual battery cells are summed up, which can obtain the availableenergy of the entire assembled battery 101. Alternatively, the availableenergy may be calculated on an assembled battery 101 basis by applyingthe calculation method described above to the entire assembled battery101.

Subsequently, a method of calculating the available energy in thisembodiment where the aforementioned concept is specifically implementedis described.

FIG. 4 shows functional blocks of the battery management apparatus 102pertaining to an available energy calculation process according to afirst embodiment of the present invention. The battery managementapparatus 102 of this embodiment includes functional blocks including abattery state calculation unit 501, a mid voltage calculation unit 502,a remaining capacity calculation unit 503, and an available energycalculation unit 504. These functional blocks can be achieved by causinga computer to execute a predetermined program, for example.

The battery state calculation unit 501 obtains current I, closed-circuitvoltage CCV, and battery temperature T_(cell) detected when theassembled battery 101 is charged or discharged, from the current sensor103, the voltage sensor 105 and the temperature sensor 106,respectively. Based on these pieces of information, state values thatare the open circuit voltage OCV, state of charge SOC, polarizationvoltage Vp, charge capacity fade SOHQ and internal resistance rise SOHR,and represent the current states of the assembled battery 101, arecalculated. Note that the details of the method of calculating thesestate values by the battery state calculation unit 501 are describedlater with reference to FIG. 5.

The mid voltage calculation unit 502 obtains the state of charge SOC andthe internal resistance rise SOHR among the state values of theassembled battery 101 calculated by the battery state calculation unit501, while obtaining the battery temperature T_(cell) from thetemperature sensor 106. Based on the obtained pieces of information, themid voltage 710 described in FIG. 3 is calculated. Note that the detailsof the method of calculating the mid voltage by the mid voltagecalculation unit 502 are described later with reference to FIG. 7.

The remaining capacity calculation unit 503 obtains the state of chargeSOC and the charge capacity fade SOHQ among the state values of theassembled battery 101 calculated by the battery state calculation unit501. Based on the obtained pieces of information, the remaining capacityof the assembled battery 101 at the present time is calculated. Notethat the details of the method of calculating the remaining capacity bythe remaining capacity calculation unit 503 are described later.

The available energy calculation unit 504 calculates the availableenergy of the assembled battery 101 based on the mid voltage calculatedby the mid voltage calculation unit 502 and the remaining capacitycalculated by the remaining capacity calculation unit 503. Specifically,as represented in the following (Expression 2), the available energy ofthe assembled battery 101 is calculated by multiplying the mid voltageby the remaining capacity.

Available energy (Wh)=mid voltage (V)×remaining capacity(Ah)  (Expression 2)

The available energy of the assembled battery 101 calculated by thebattery management apparatus 102 is transmitted from the batterymanagement apparatus 102 to the upper level controller 4, and is used tocontrol the inverter 2. Accordingly, the available energy of theassembled battery 101 is calculated in real time in the battery energystorage system 1, and charge and discharge control of the assembledbattery 101 is performed.

FIG. 5 shows functional blocks of the battery state calculation unit501. The battery state calculation unit 501 includes a battery modelunit 601, and a state-of-health detection unit 602.

The battery model unit 601 stores a battery model obtained by modelingthe assembled battery 101, and obtains the open circuit voltage OCV, thestate of charge SOC, and the polarization voltage Vp, using this batterymodel. The battery model in the battery model unit 601 is configureddepending on the numbers of serial couplings and parallel couplings ofbattery cells in the actual assembled battery 101, and the equivalentcircuit of each battery cell, for example. The battery model unit 601can obtain the open circuit voltage OCV, the state of charge SOC and thepolarization voltage Vp depending on the state of the assembled battery101, by applying, to this battery model, the current I, theclosed-circuit voltage CCV and the battery temperature T_(cell) obtainedrespectively from the current sensor 103, the voltage sensor 105 and thetemperature sensor 106.

FIG. 6 shows an example of the equivalent circuit of the battery cell inthe battery model configured in the battery model unit 601. Theequivalent circuit of the battery cell shown in FIG. 6 includes an openvoltage source 603 having a voltage value Voc, an internal resistance604 having a resistance value R, and a polarization model as a parallelcircuit which includes a polarization capacity 605 having a capacitancevalue Cp and a polarization resistance 606 having a resistance value Rp;these components are coupled in series. In this equivalent circuit, thevoltage across the opposite ends of the open voltage source 603, i.e.,the voltage value Voc, corresponds to the open circuit voltage OCV, andthe voltage across the opposite ends of the parallel circuit of thepolarization capacity 605 and the polarization resistance 606corresponds to the polarization voltage Vp. A value obtained by addingapplied voltage I×R at the internal resistance 604 and the polarizationvoltage Vp when the current I flows through the equivalent circuit, tothe open circuit voltage OCV, corresponds to the closed-circuit voltageCCV. Furthermore, the value of each circuit constant in the equivalentcircuit in FIG. 6 is defined depending on the battery temperatureT_(cell). Accordingly, based on these relationships, the battery modelunit 601 can obtain the open circuit voltage OCV and the polarizationvoltage Vp of the entire assembled battery 101 from the current I, theclosed-circuit voltage CCV and the battery temperature T_(cell), andfurther obtain the state of charge SOC from the calculation result ofthe open circuit voltage OCV.

Returning to the description on FIG. 5, the state-of-health detectionunit 602 detects the state of health of the assembled battery 101, andobtains the charge capacity fade SOHQ and the internal resistance riseSOHR depending on the state of health. Each battery cell of theassembled battery 101 progressively deteriorates by being repetitivelycharged and discharged. Depending on the state of health, reduction incharge capacity and increase in internal resistance occur. Thestate-of-health detection unit 602 preliminarily stores, for example,information representing the relationship between the current, voltageand temperature and the state of health of the assembled battery 101,and detects the state of health of the assembled battery 101, throughuse of this information, based on the current I, the closed-circuitvoltage CCV and the battery temperature T_(cell) obtained respectivelyfrom the current sensor 103, the voltage sensor 105 and the temperaturesensor 106. Based on the preliminarily stored relationship between thestate of health, charge capacity fade SOHQ and internal resistance riseSOHR, the charge capacity fade SOHQ and internal resistance rise SOHRthat correspond to the detection result of the state of health of theassembled battery 101 can be obtained.

FIG. 7 shows functional blocks of the mid voltage calculation unit 502according to the first embodiment of the present invention. The midvoltage calculation unit 502 includes a mid OCV table group 607, a midDCR table group 608, and a discharge current setting unit 609.

The state of charge SOC obtained from the battery state calculation unit501, and the battery temperature T_(cell) obtained from the temperaturesensor 106 are each input into the mid OCV table group 607 and the midDCR table group 608. Based on the input pieces of information, the midOCV table group 607 and the mid DCR table group 608 obtain the mid OCVand the mid DCR depending on the current state of the assembled battery101 through table search. Note that the mid DCR is a DC resistance valueof the assembled battery 101 corresponding to the mid voltage.

In the mid OCV table group 607, MidOCV indicating the value of the midOCV is set for each combination of the state of charge SOC and thebattery temperature T_(cell). For example, the value of the batterytemperature T_(cell) is represented as T_(i) (i=1 to p), and the valueof the state of charge SOC is represented as SOC_(j) (j=1 to q). Withrespect to each combination thereof, p×q voltage values MidOCV_(i,j) (V)represented by the following (Expression 3) are set in the mid OCV tablegroup 607.

MidOCV_(i,j)=MidOCV(T _(i),SOC_(j))  (Expression 3)

In the mid DCR table group 608, MidDCR indicating the value of the midDCR for each combination of the state of charge SOC and the batterytemperature T_(cell), is set. For example, the value of the batterytemperature T_(cell) is represented as T_(i) (i=1 to p), and the valueof the state of charge SOC is represented as SOC_(j) (j=1 to q). Withrespect to each combination thereof, p×q resistance values MidDCR_(i,j)(Ω) represented by the following (Expression 4) are set in the mid DCRtable group 608.

MidDCR_(i,j)=MidDCR(T _(i),SOC_(j))  (Expression 4)

Note that each of the values of MidOCV_(i,j) in the mid OCV table group607, and each of the values of MidDCR_(i,j) in the mid DCR table group608 can be preset based on an analysis result on a discharge test resultof the assembled battery 101, and on a result of simulation using anequivalent circuit model of the assembled battery 101. For example,these preset values are written into a memory, not shown, included inthe battery management apparatus 102, thereby allowing the mid OCV tablegroup 607 and the mid DCR table group 608 to be formed in the batterymanagement apparatus 102.

The mid voltage calculation unit 502 obtains what corresponds to theinput current state of charge SOC and battery temperature T_(cell) ofthe assembled battery 101 among the voltage values MidOCV_(i,j) and theresistance values MidDCR_(i,j) represented by (Expression 3) and(Expression 4), from the mid OCV table group 607 and the mid DCR tablegroup 608, respectively. The mid voltage described with reference toFIG. 3 is calculated by the following (Expression 5), based on theobtained values, the discharge current I_(C0,DCh) preset in thedischarge current setting unit 609, and the input internal resistancerise SOHR.

MidVoltage(t)=MidOCV(t)−I _(C0,DCh)×MidDCR(t)×SOHR(t)/100   (Expression5)

In (Expression 5), MidVoltage(t) represents the value of the mid voltageat the current time t. MidOCV(t) and MidDCR(t) respectively representthe values of the mid OCV and the mid DCR at the current time t, and arerespectively obtained from the mid OCV table group 607 and the mid DCRtable group 608. SOHR(t) represents the value of the internal resistancerise SOHR calculated by the battery state calculation unit 501 at thetime t.

Note that MidOCV(t) and MidDCR(t) in (Expression 5), i.e., the values ofthe mid OCV and the mid DCR corresponding to the current state of chargeSOC and battery temperature T_(cell), may be obtained, throughinterpolation, from the mid OCV table group 607 and the mid DCR tablegroup 608. For example, interpolation using any of various knowninterpolation methods, such as linear interpolation, Lagrangeinterpolation, and nearest neighbor interpolation, can be performed.Accordingly, even for a combination of the state of charge SOC and thebattery temperature T_(cell) that is not described in the mid OCV tablegroup 607 or the mid DCR table group 608, an appropriate voltage valueand resistance value as the mid OCV and the mid DCR can be obtained.

For example, it is assumed that the values of the state of charge SOCand the battery temperature T_(cell) at the time t are represented asSOC(t) and T_(cell)(t), respectively, and these satisfy therelationships in the following (Expression 6). In this case, MidOCV(t)and MidDCR(t) corresponding to the combination of SOC(t) and T_(cell)(t)are not described in the mid OCV table group 607 or the mid DCR tablegroup 608.

T _(i) <T _(cell)(t)<T _(i+1)

SOC_(j)<SOC(t)<SOC_(j+1)  (Expression 6)

In the case described above, the mid voltage calculation unit 502 canobtain MidOCV(t) at the time t by the following (Expression 7), throughinterpolation, from the four types of voltage values corresponding tofour combinations that combine T_(i) or T_(i+1) and SOC_(j) or SOC_(j+1)in the mid OCV table group 607, i.e., MidOCV_(i,j), MidOCV_(i+1,j),MidOCV_(i,j+1) and MidOCV_(i+1,j+1).

MidOCV(t)=f(SOC(t)T_(cell)(t)MidOCV_(i,j),MidOCV_(i+1,j),MidOCV_(i,j+1),MidOCV_(i+1,j+1))  (Expression7)

The mid voltage calculation unit 502 can obtain MidDCR(t) at the time tby the following (Expression 8), through interpolation, from the fourtypes of resistance values corresponding to four combinations thatcombine T_(i) or T_(i+1) and SOC_(j) or SOC_(j+1) in the mid DCR tablegroup 608, i.e., MidDCR_(i,j), MidDCR_(i+1,j), MidDCR_(i,j+1) andMidDCR_(i+1,j+1).

MidDCR(t)=g(SOC(t)T_(cell)(t)MidDCR_(i,j),MidDCR_(i+1,j),MidDCR_(i,j+1),MidDCR_(i+1,j+1))  (Expression8)

In (Expression 7) and (Expression 8), f and g represent interpolationprocesses executed for the mid OCV table group 607 and the mid DCR tablegroup 608, respectively. The details of these processes vary dependingon the interpolation method in the case of interpolation.

After MidOCV(t) and MidDCR(t) through interpolation are successfullyobtained as described above, the mid voltage calculation unit 502applies these values to (Expression 5) described above, thereby allowingthe mid voltage MidVoltage(t) at the current time t to be calculated.

The remaining capacity calculation unit 503 calculates the remainingcapacity of the assembled battery 101 by the following (Expression 9)based on the state of charge SOC and the charge capacity fade SOHQobtained from the battery state calculation unit 501.

RemainingCapacity(t)=(SOC(t)−SOC_(min))/100×Ah_(rated)×SOHQ(t)/100  (Expression 9)

In (Expression 9), RemainingCapacity(t) represents the value of theremaining capacity at the current time t. Ah_(rated) represents therated capacity of the assembled battery 101, i.e., the remainingcapacity of the assembled battery 101 at the start of use when beingfully charged.

The first embodiment of the present invention described above exerts thefollowing working effects.

(1) The battery management apparatus 102 is an apparatus which managesthe chargeable and dischargeable assembled battery 101, and includes:the battery state calculation unit 501 which calculates the state ofcharge SOC representing the state of charge of the assembled battery101, and the charge capacity fade SOHQ representing the deteriorationdegree; the mid voltage calculation unit 502 which calculates the midvoltage 710, i.e., MidVoltage(t), which is present between the voltagevalue 704 representing the discharge voltage in the current state ofcharge of the assembled battery 101, and the voltage value 706representing the discharge voltage in the minimum state of chargeSOC_(min); the remaining capacity calculation unit 503 which calculatesthe remaining capacity of the assembled battery 101, i.e.,RemainingCapacity(t), based on the state of charge SOC and the chargecapacity fade SOHQ; and the available energy calculation unit 504 whichcalculates the available energy of the assembled battery 101, based onthe mid voltage and the remaining capacity. Accordingly, the availableenergy of the assembled battery 101 can be correctly estimated.

(2) As shown in FIG. 3, the mid voltage 710 is a voltage at which thevalue obtained by multiplying the mid voltage 710 by the remainingcapacity matches the integral value of the discharge curve 701representing change in discharge voltage from the current state ofcharge SOC to the minimum state of charge SOC_(min). The availableenergy calculation unit 504 calculates the available energy bymultiplying the mid voltage by the remaining capacity using (Expression2). Accordingly, even when the discharge current changes, the availableenergy of the assembled battery 101 can be calculated in real time.

(3) The mid voltage calculation unit 502 includes: the mid OCV tablegroup 607 where the voltage value MidOCV_(i,j) is set for eachcombination of the state of charge SOC and the battery temperatureT_(cell) of the assembled battery 101; and the mid DCR table group 608where the resistance value MidDCR_(i,j) is set for each combination ofthe state of charge SOC and the battery temperature T_(cell) of theassembled battery 101. The voltage value MidOCV(t) and the resistancevalue MidDCR(t) corresponding to the state of charge SOC(t) calculatedby the battery state calculation unit 501 and the current batterytemperature T_(cell)(t) of the assembled battery 101 are then obtainedfrom the mid OCV table group 607 and the mid DCR table group 608. Basedon the obtained voltage value MidOCV(t) and resistance value MidDCR(t),the mid voltage MidVoltage(t) is calculated. Accordingly, the midvoltage depending on the state of the assembled battery 101 can beeasily and correctly calculated.

(4) The mid voltage calculation unit 502 can also obtain the voltagevalue MidOCV(t) and the resistance value MidDCR(t) corresponding to thestate of charge SOC(t) calculated by the battery state calculation unit501 and the current battery temperature T_(cell) (t) of the assembledbattery 101, through interpolation, from the mid OCV table group 607 andthe mid DCR table group 608. Accordingly, also for any combination ofthe state of charge SOC and the battery temperature T_(cell) that is notdescribed in the mid OCV table group 607 or the mid DCR table group 608,the voltage value MidOCV(t) and the resistance value MidDCR(t)corresponding thereto can be finely obtained.

Second Embodiment

Next, a second embodiment of the present invention is described. In thisembodiment, instead of the constant discharge current I_(C0,DCh)described in the first embodiment, a method is described whichcalculates the available energy of the assembled battery 101 by usingdischarge current I_(Ck,DCh) determined in consideration of an actualtraveling state of a vehicle provided with the assembled battery 101.Note that a configuration of a battery energy storage system accordingto this embodiment is similar to the battery energy storage system(BESS) 1 in FIG. 1 described in the first embodiment. Accordingly, thedescription thereof is omitted.

In this embodiment, unlike the discharge current I_(C0,DCh) in the firstembodiment, the value of the discharge current I_(Ck,DCh) is not apreset value, and is determined by the battery management apparatus 102based on an immediately previous traveling state of the vehicle. Thatis, the available energy of the assembled battery 101 in this embodimentcorresponds to the total electric energy (Wh) dischargeable without eachbattery cell falling below the minimum voltage V_(min), until SOC ofeach battery cell reaches SOC_(min) which is the minimum SOC valuepermitted for the corresponding battery cell, in a case where eachbattery cell of the assembled battery 101 is discharged with thedischarge current I_(Ck,DCh).

FIG. 8 shows functional blocks of the battery management apparatus 102pertaining to an available energy calculation process according to thesecond embodiment of the present invention. The battery managementapparatus 102 of this embodiment includes functional blocks including abattery state calculation unit 501, a mid voltage calculation unit 502a, a remaining capacity calculation unit 503, an available energycalculation unit 504, and a C-rate calculation unit 505. Thesefunctional blocks can be achieved by causing a computer to execute apredetermined program, for example.

The battery state calculation unit 501, the remaining capacitycalculation unit 503 and the available energy calculation unit 504 inFIG. 8 are similar to those in the battery management apparatus 102 inFIG. 4 described in the first embodiment. Accordingly, hereinafter, theoperations of the mid voltage calculation unit 502 a in FIG. 8 providedinstead of the mid voltage c calculation unit 502 in FIG. 2, and thenewly provided C-rate calculation unit 505 are mainly described, anddescription of the other functional blocks in FIG. 8 is omitted.

The C-rate calculation unit 505 calculates the C-rate during dischargeof the assembled battery 101, i.e., the rate of the magnitude of thedischarge current to the capacitance of the assembled battery 101. Forexample, measured values of discharge current obtained from apredetermined time period before to the present time are averaged, andthe average value is divided by the rated capacity of the assembledbattery 101, thereby calculating the C-rate during discharge. The valueof the C-rate calculated by the C-rate calculation unit 505 is inputinto the mid voltage calculation unit 502 a.

The mid voltage calculation unit 502 a obtains the state of charge SOCand the internal resistance rise SOHR among the state values of theassembled battery 101 calculated by the battery state calculation unit501, while obtaining the battery temperature T_(cell) from thetemperature sensor 106. Furthermore, the C-rate is obtained from theC-rate calculation unit 505. Based on the obtained pieces ofinformation, the mid voltage 710 described in FIG. 3 in the firstembodiment is calculated.

FIG. 9 shows the functional blocks of the mid voltage calculation unit502 a according to the second embodiment of the present invention. Themid voltage calculation unit 502 a includes a mid OCV table group 610, amid DCR table group 611, and a gain setting unit 612.

The state of charge SOC obtained from the battery state calculation unit501, the battery temperature T_(cell) obtained from the temperaturesensor 106 and the C-rate obtained from the C-rate calculation unit 505are input into the mid OCV table group 610 and the mid DCR table group611. Based on the input pieces of information, the mid OCV table group610 and the mid DCR table group 611 obtain the mid OCV and the mid DCRdepending on the current state of the assembled battery 101 throughtable search.

In the mid OCV table group 610, MidOCV indicating the value of the midOCV is set for each combination of the C-rate, the state of charge SOCand the battery temperature T_(cell). Specifically, multiple tables ineach of which the value of MidOCV is set for each combination of thestate of charge SOC and the battery temperature T_(cell), are setdepending on the value of the C-rate. For example, it is assumed thatthe value of the C-rate is represented as C_(k) (k=1 to N). Tablessimilar to the mid OCV table group 607 described in the first embodimentare set with respect to each C_(k), and the total number thereof is N.The value of MidOCV in each table is set to a value at the correspondingC_(k).

Likewise, in the mid DCR table group 611, MidDCR indicating the value ofthe mid DCR is set for each combination of the C-rate, the state ofcharge SOC and the battery temperature T_(cell). Specifically, multipletables in each of which the value of MidDCR is set for each combinationof the state of charge SOC and the battery temperature T_(cell), are setdepending on the value of the C-rate. That is, as described above, it isassumed that the value of the C-rate is represented as C_(k) (k=1 to N).Tables similar to the mid DCR table group 608 described in the firstembodiment are set with respect to each C_(k), and the total numberthereof is N. The value of MidDCR in each table is set to a value atcorresponding C_(k).

The mid voltage calculation unit 502 a obtains the values of the mid OCVand the mid DCR corresponding to the input current state of charge SOC,battery temperature T_(cell) and value of the C-rate of the assembledbattery 101, from the mid OCV table group 610 and the mid DCR tablegroup 611.

The gain setting unit 612 sets the rated capacity Ah_(rated) in(Expression 9) described in the first embodiment, as the gain for theinput C-rate. By multiplying the value of the C-rate by the ratedcapacity Ah_(rated), the discharge current I_(Ck,DCh) is calculated.

The mid voltage calculation unit 502 a calculates the mid voltagedescribed with reference to FIG. 3 by the following (Expression 10)based on the values of the mid OCV and the mid DCR obtained respectivelyfrom the mid OCV table group 610 and the mid DCR table group 611, andthe discharge current I_(Ck,DCh) output from the gain setting unit 612and the input internal resistance rise SOHR. Here, provided that thevalue of the C-rate at the current time t is represented as C(t),I_(Ck,DCh)=C(t)×Ah_(rated).

MidVoltage(t)=MidOCV(t)−I _(Ck,DCh)×MidDCR(t)×SOHR(t)/100  (Expression10)

Similar to (Expression 5) described in the first embodiment,MidVoltage(t) represents the value of the mid voltage at the currenttime t in (Expression 10). MidOCV(t) and MidDCR(t) respectivelyrepresent the values of the mid OCV and the mid DCR at the current timet, and are respectively obtained from the mid OCV table group 610 andthe mid DCR table group 611. SOHR(t) represents the value of theinternal resistance rise SOHR calculated by the battery statecalculation unit 501 at the time t.

Similar to the first embodiment, also in this embodiment, MidOCV(t) andMidDCR(t) in (Expression 10), i.e., the values of the mid OCV and themid DCR corresponding to the current state of charge SOC and batterytemperature T_(cell), may be obtained, through interpolation, from themid OCV table group 610 and the mid DCR table group 611. Accordingly,even for a combination of the C-rate, the state of charge SOC andbattery temperature T_(cell) that is not described in the mid OCV tablegroup 610 or the mid DCR table group 611, an appropriate voltage valueand resistance value as the mid OCV and the mid DCR can be obtained.

For example, it is assumed that the state of charge SOC, the batterytemperature T_(cell) and the values of the C-rate at the time t arerepresented as SOC(t), T_(cell) (t) and C(t), respectively, and thesesatisfy the relationships in the following (Expression 11). In thiscase, MidOCV(t) and MidDCR(t) corresponding to the combination ofSOC(t), T_(cell)(t) and C(t) are not described in the mid OCV tablegroup 610 or the mid DCR table group 611.

T _(i) <T _(cell)(t)<T _(i+1)

SOC_(j)<SOC(t)<SOC_(j+1)

C _(k) <C(t)<C _(k+1)  (Expression 11)

In the above description, first, the mid voltage calculation unit 502 acalculates a table corresponding to C(t), through interpolation, fromtwo tables corresponding to C_(k) and C_(k+1) in the mid OCV table group610. In the calculated table, four types of voltage values correspondingto four combinations that combine T_(i) or T_(i+1) and SOC_(j) orSOC_(j+1) are extracted as MidOCV_(i,j) (C_(k), C_(k+1))MidOCV_(i+1,j)(C_(k), C_(k+1)) MidOCV_(i,j+1)(C_(k), C_(k+1)), andMidOCV_(i+1,j+1) (C_(k), C_(k+1)). From these voltage values, MidOCV(t)at the time t can be obtained by the following (Expression 12), throughinterpolation.

MidOCV(t)=f(SOC(t),T _(cell)(t)MidOCV_(i,j)(C _(k) ,C_(k+1))MidOCV_(i+1,j)(C _(k) ,C _(k+1)),MidOCV_(i,j+1)(C _(k) ,C_(k+1)),MidOCV_(i+1,j+1)(C _(k) ,C _(k+1)))   (Expression 12)

The mid voltage calculation unit 502 a calculates a table correspondingto C(t), through interpolation, from two tables corresponding to C_(k)and C_(k+1) in the mid DCR table group 611. In the calculated table,four types of resistance values corresponding to four combinations thatcombine T_(i) or T_(i+1) and SOC or SOC_(j+1) are extracted asMidDCR_(i,j) (C_(k), C_(k+1)) MidDCR_(i+1,j) (C_(k), C_(k+1)),MidDCR_(i,j+1)(C_(k), C_(k+1)), and MidDCR_(i+1,j+1) (C_(k), C_(k+1)).From these resistance values, MidDCR(t) at the time t can be obtained bythe following (Expression 13), through interpolation.

MidDCR(t)=g(SOC(t)T _(cell)(t)MidDCR_(i,j)(C _(k) ,C_(k+1)),MidDCR_(i+1,j)(C _(k) ,C _(k+1)), and MidDCR_(i,j+1)(C _(k) ,C_(k+1)),MidDCR_(i+1,j+1)(C _(k) ,C _(k+1)))  (Expression 13)

After MidOCV(t) and MidDCR(t) through interpolation are successfullyobtained as described above, the mid voltage calculation unit 502 aapplies these values to (Expression 10) described above, therebyallowing the mid voltage MidVoltage(t) at the current time t to becalculated.

According to the aforementioned second embodiment of the presentinvention, in addition to the working effects (1) and (2) described inthe first embodiment, the following working effects are further exerted.

(5) The battery management apparatus 102 includes the C-rate calculationunit 505 which calculates the C-rate when the assembled battery 101 isdischarged. The mid voltage calculation unit 502 a calculates the midvoltage 710 by using the C-rate calculated by the C-rate calculationunit 505. Accordingly, in consideration of the actual traveling state ofthe vehicle provided with the assembled battery 101, the mid voltage 710can be appropriately calculated.

(6) The mid voltage calculation unit 502 a includes: the mid OCV tablegroup 610 where the voltage value MidOCV_(i,j) is set for eachcombination of the C-rate, the state of charge SOC and the batterytemperature T_(cell) of the assembled battery 101; and the mid DCR tablegroup 611 where the resistance value MidDCR_(i,j) is set for eachcombination of the C-rate, the state of charge SOC and the batterytemperature T_(cell) of the assembled battery 101. The voltage valueMidOCV(t) and the resistance value MidDCR(t) corresponding to the C-ratevalue calculated by the C-rate calculation unit 505, the state of chargeSOC(t) calculated by the battery state calculation unit 501 and thecurrent battery temperature T_(cell)(t) of the assembled battery 101 arethen obtained from the mid OCV table group 610 and the mid DCR tablegroup 611. Based on the obtained voltage value MidOCV(t) and resistancevalue MidDCR(t), the mid voltage MidVoltage(t) is calculated.Accordingly, the mid voltage depending on the state of the assembledbattery 101 can be easily and correctly calculated.

(7) The mid voltage calculation unit 502 a can also obtain the voltagevalue MidOCV(t) and the resistance value MidDCR(t) corresponding to theC-rate value C(t) calculated by the C-rate calculation unit 505, thestate of charge SOC(t) calculated by the battery state calculation unit501 and the current battery temperature T_(cell) (t) of the assembledbattery 101, through interpolation, from the mid OCV table group 610 andthe mid DCR table group 611. Accordingly, also for any combination ofthe C-rate, the state of charge SOC and the battery temperature T_(cell)that is not described in the mid OCV table group 610 or the mid DCRtable group 611, the voltage value MidOCV(t) and the resistance valueMidDCR(t) corresponding thereto can be finely obtained.

Note that in each embodiment described above, application examples tothe battery energy storage systems mounted on electric vehicles, hybridvehicles and the like have been described. Likewise, the presentinvention is applicable also to battery energy storage systems used forother applications, for example, battery energy storage systems and thelike coupled to a power grid and used.

In each embodiment described above, the method of calculating theavailable energy when the assembled battery 101 is discharged isdescribed. Alternatively, similar calculation methods are alsoapplicable to chargeable energy when the assembled battery 101 ischarged. Here, the chargeable energy is defined as the total amount ofelectrical energy chargeable when the assembled battery 101 is chargedfrom a certain state of charge. This corresponds to the total electricenergy (Wh) with which each battery cell can be charged until SOC ofeach battery cell reaches SOC_(max), which is the maximum SOC valuepermitted for the corresponding battery cell, in a case where eachbattery cell of the assembled battery 101 is charged with a constantdischarge current.

In the case of application to calculation of the chargeable energy, themid voltage 710 described with reference to FIG. 3 is present betweenthe voltage value corresponding to the current SOC and the voltage valuecorresponding to SOC_(max) when charging is completed, on a charge curverepresenting change in charge voltage from the current SOC of theassembled battery 101 to the SOC_(max). The mid voltage 710 is thenobtained such that a value obtained by multiplying the mid voltage 710by the chargeable capacity defined as the difference between the currentSOC and SOC_(max) matches the integral value of the charge curve fromthe current SOC to SOC_(max). Specifically, the mid voltage duringcharging can be obtained by using those similar to the mid voltagecalculation unit 502 described in the first embodiment, and the midvoltage calculation unit 502 a described in the second embodiment. Notethat the mid voltage (CCV) during charging increases in voltage by whatis for the internal resistance more than the mid OCV. Accordingly,(Expression 5) and (Expression 10) described above may be changed to thefollowing (Expression 5′) and (Expression 10′) and used.

MidVoltage(t)=MidOCV(t)+I _(C0,DCh)×MidDCR(t)×SOHR(t)/100   (Expression5′)

MidVoltage(t)=MidOCV(t)+I _(Ck,DCh)×MidDCR(t)×SOHR(t)/100  (Expression10′)

The mid voltage during charging obtained as described above ismultiplied by the chargeable capacity obtained by the following(Expression 14), thereby allowing the chargeable energy to becalculated. Note that in (Expression 14), ChargeableCapacity(t)represents the value of the chargeable capacity at the current time t.Ah_(rated) represents the rated capacity of the assembled battery 101,i.e., the remaining capacity of the assembled battery 101 at the startof use when being fully charged.

ChargeableCapacity(t)=(SOC_(max)−SOC(t))/100×Ah_(rated)×SOHQ(t)/100  (Expression 14)

The present invention is not limited to the embodiments and modifiedexamples described above. Various changes can be made in a range withoutdeparting from the spirit of the present invention.

REFERENCE SIGNS LIST

-   1 Battery energy storage system (BESS)-   2 Inverter-   3 Load-   4 Upper level controller-   101 Assembled battery-   102 Battery management apparatus-   103 Current sensor-   104 Cell controller-   105 Voltage sensor-   106 Temperature sensor-   107 Relay-   501 Battery state calculation unit-   502, 502 a Mid voltage calculator-   503 Remaining capacity calculation unit-   504 Available energy calculation unit-   505 C-rate calculation unit-   601 Battery model unit-   602 State-of-health detection unit-   603 Open voltage source-   604 Internal resistance-   605 Polarization capacity-   606 Polarization resistance-   607 Mid OCV table group-   608 Mid DCR table group-   609 Discharge current setting unit-   610 Mid OCV table group-   611 Mid DCR table group-   612 Gain setting unit

1. A battery management apparatus for managing a chargeable anddischargeable battery, comprising: a battery state calculation unitwhich calculates a state of charge and a deterioration degree of thebattery; a mid voltage calculation unit which calculates a mid voltagethat is present between a charge-discharge voltage in a current state ofcharge of the battery, and a charge-discharge voltage in a minimum stateof charge or a maximum state of charge of the battery; a remainingcapacity calculation unit which calculates a remaining capacity or achargeable capacity of the battery, based on the state of charge and thedeterioration degree; and an available energy calculation unit whichcalculates available energy or chargeable energy of the battery, basedon the mid voltage and the remaining capacity, or on the mid voltage andthe chargeable capacity.
 2. The battery management apparatus accordingto claim 1, wherein the mid voltage is a voltage at which a valueobtained by multiplying the mid voltage by the remaining capacity or thechargeable capacity matches an integral value of a charge and dischargecurve representing change in the charge-discharge voltage from thecurrent state of charge to the minimum state of charge or the maximumstate of charge, and the available energy calculation unit calculatesthe available energy or the chargeable energy by multiplying the midvoltage by the remaining capacity or the chargeable capacity.
 3. Thebattery management apparatus according to claim 1, wherein the midvoltage calculation unit includes: a first table in which a voltagevalue is set for each combination of the state of charge and atemperature of the battery; and a second table in which a resistancevalue is set for each combination of the state of charge and thetemperature of the battery, obtains the voltage value and the resistancevalue corresponding to the state of charge calculated by the batterystate calculation unit and the current temperature of the battery,respectively from the first table and the second table, and calculatesthe mid voltage, based on the obtained voltage value and the resistancevalue.
 4. The battery management apparatus according to claim 3, whereinthe mid voltage calculation unit obtains the voltage value and theresistance value corresponding to the state of charge calculated by thebattery state calculation unit and the current temperature of thebattery, through interpolation, respectively from the first table andthe second table.
 5. The battery management apparatus according to claim1, further comprising a C-rate calculation unit which calculates aC-rate when the battery is charged or discharged, wherein the midvoltage calculation unit calculates the mid voltage by using the C-ratecalculated by the C-rate calculation unit.
 6. The battery managementapparatus according to claim 5, wherein the mid voltage calculation unitincludes: a first table in which a voltage value is set for eachcombination of the C-rate and the state of charge and a temperature ofthe battery; and a second table in which a resistance value is set foreach combination of the C-rate and the state of charge and thetemperature of the battery, obtains the voltage value and the resistancevalue corresponding to the C-rate calculated by the C-rate calculationunit, the state of charge calculated by the battery state calculationunit, and the current temperature of the battery, respectively from thefirst table and the second table, and calculates the mid voltage, basedon the obtained voltage value and the resistance value.
 7. The batterymanagement apparatus according to claim 6, wherein the mid voltagecalculation unit obtains the voltage value and the resistance valuecorresponding to the C-rate calculated by the C-rate calculation unit,the state of charge calculated by the battery state calculation unit,and the current temperature of the battery, through interpolation,respectively from the first table and the second table.
 8. A batterymanagement method for managing a chargeable and dischargeable battery,the method comprising, by a computer: calculating a state of charge anda deterioration degree of the battery; calculating a mid voltage that ispresent between a charge-discharge voltage in a current state of chargeof the battery, and a charge-discharge voltage in a minimum state ofcharge or a maximum state of charge of the battery; calculating aremaining capacity or a chargeable capacity of the battery, based on thecalculated state of charge and deterioration degree; and calculatingavailable energy or chargeable energy of the battery, based on thecalculated mid voltage and remaining capacity, or on the calculated midvoltage and chargeable capacity.
 9. A battery energy storage system,comprising: the battery management apparatus according to claim 1; achargeable and dischargeable battery; and a charge-discharge apparatuswhich charges and discharges the battery, based on available energy orchargeable energy of the battery calculated by the battery managementapparatus.